Your wording seems to be a bit misleading. It is normally said that it was an expansion OF spacetime, not in spacetime. And of course the "size" of the universe is getting bigger. If it's expanding, how could it not be getting bigger? An infinite universe (unknown to be the case) does not mean it has any particular size. It means, AFAIK, as time goes on, whatever size it is increases without end. The amount of baryonic and dark matter in the universe is apparently finite. No more of this stuff is appearing within the universe. As space continues to expand, the density of matter continues to decrease. This would seem to argue against "exact duplicates" in some distant region of the universe. Even if the "whole universe" is 1023 times larger than the portion that is visible to us, as Alan Guth originally estimated, that is nowhere near the size required to run into a duplicate of our galaxy, which, per Tegmark, is more like 101028 meters from here.
Originally Posted by Reality Check
Everyone is entitled to his own opinion, but not his own facts.